After drilling more than two miles into the ground in a remote area of central California, scientists said Thursday that they have hit pay dirt – the first rocks ever to be obtained from deep within the San Andreas Fault.

Experts believe the cylindrical samples, which have been washed, shrink-wrapped and gently tucked away in refrigerators for safekeeping, may hold many secrets about earthquakes and the 800-mile-long fault line responsible for the Bay Area’s devastating 1906 earthquake.

Why do earthquakes start? How do they stop? What is the fault made of?Scientists believe that by studying the new rock samples they’ll be able to come up with answers for some of the tough questions that have eluded them for years.

“This for us is really the mother lode,” said William Ellsworth, a geophysicist with the U.S. Geological Survey in Menlo Park. “They’re more precious than moon rocks and gold.”

The samples, taken from 2 1/2 miles beneath the surface of the San Andreas Fault, are the first rocks ever to be obtained from deep within an actively moving fault zone responsible for some of the world’s most damaging earthquakes.

The project, with a budget of about $25 million, has been 15 years in the making. After drilling close to the fault in 2004 and 2005, geologists worked 24 hours a day, seven days a week last summer to retrieve 135 feet of rock cores, each measuring four inches in diameter. The last of the samples was brought to the surface in the pre-dawn hours of Sept. 7. The scientists unveiled the rock samples on Thursday.

“For the very first time, scientists can hold the San Andreas Fault in their hands,” said Mark Zoback, a professor of earth sciences and geophysics at Stanford University. “It’s a new beginning for several different areas of earthquake research.”

Researchers aren’t optimistic that the dark-gray chunks of rock will help them predict when the “Big One” is about to occur. But they will now know exactly what the fault is made of, which they hope will answer questions about the mechanics of earthquakes.

Hundreds of scientists from around the world are expected to submit requests to study the samples, yet it will likely be years before they understand what the rocks have to say about the physics of earthquakes.

“The ultimate goal is to understand how faults work,” Ellsworth said.

The drilling has all occurred about 23 miles northeast of Paso Robles near the small town of Parkfield. The site was selected because it’s an especially active part of the San Andreas Fault that moves regularly, but does not produce large earthquakes.

Researchers can already see from the samples that chunks of serpentine are embedded within them. Serpentine is a green-colored mineral which scientists have long suspected might be one of the reasons why that stretch of the San Andreas Fault silently creeps. But it had never been proven that the substance was indeed in the fault.

Scientists wonder if the serpentine has been literally smoothing the way for huge tectonic plates to slide silently past one another.

During earlier drilling in 2005, mineralogist Diane Moore of the USGS detected talc in the rock cuttings. Talc is a slippery mineral best known for its use on babies’ bottoms. It can be produced when serpentine comes into contact with water.

“We’ve only really just begun the study of these rocks,” Ellsworth said.

During the next phase of the project, scientists will create the world’s first underground earthquake observatory that is within an active fault. They will lower into it a number of seismic instruments that will await and observe dozens of small earthquakes and their aftershocks over the next 10 to 20 years. That phase of the project could help scientists determine whether earthquakes are predictable.

The drilling, which first broke ground in 2004, hasn’t always been easy. And at times, scientists concede, they wondered if they might end up empty-handed.

The drilling equipment – the same kind used to drill oil wells in California – failed at times this summer as it faced the daunting task of burrowing into thick rock far below the Earth’s surface, where temperatures reached 240 degrees. Then, on the very day scientists had hoped to retrieve their first samples, a major lightning storm swept through the area, threatening their work.

As the geologists were able to raise that very first tubular slice of the fault, it was, said Zoback, a true “eureka moment.”

And the samples are being protected as if they were gold bars in Fort Knox. The rocks are being kept moist and refrigerated at a chilly 34 degrees to prevent the cores and fluid in them from being disturbed.

The collection represents a major career geologic milestone for many of those involved.

“This is something we’ve been dreaming about achieving for many years,” Ellsworth said. “It’s not unlike the people who dreamed about bringing rocks from the moon or Mars.”

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